Integrated circuits may be subject to different types of security attacks. For example, integrated circuits used for decoding and displaying digital television signals such as, for example, set-top box (STB) chips may be hacked by users seeking to access, for free, subscription-services or pay-for-service programming for television. In addition to viewing the programming without paying, successful hackers may be able to distribute “in-the-clear” video content to others.
A hacker may attempt to target different elements of a system. For example, a hacker may target a software component of an STB chip. If software developed by the hacker can be downloaded onto the STB chip, then on-chip security may be overridden in a variety of ways. In response to such attacks, some STB chips may perform a one-time integrity check on a software code set to ensure, for example, that the software originated from an authorized or recognized source. However, a one-time software integrity check may be open to attacks that may occur after the one-time integrity check has been completed.
Some STB chips may encrypt software instructions in a flash memory or a synchronous dynamic random access memory (SDRAM) memory using data encryption standard (DES) encryption or triple DES (3DES) encryption. By using a DES or 3DES encryption key known only to an authorized entity and the STB, the STB can be assured, with a high degree of confidence, that only microprocessor instructions from an authorized source can be decoded properly. Instruction encryption using DES or 3DES may also protect the code base from examination for clues relating to internal chip operation, even if the flash memory is removed from the board and examined separately. However, DES decryption or 3DES decryption of microprocessor instructions may suffer from, for example, latencies induced in a pipeline to a microprocessor. Pipeline latencies may substantially reduce throughput.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of ordinary skill in the art through comparison of such systems with one or more aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.